A caffeine/ryanodine-sensitive Ca2+ pool is involved in triggering spontaneous variations of Ca2+ in Jurkat T lymphocytes by Ca2+-induced Ca2+ release (CICR) mechanism

Caffeine and ryanodine triggered an increase in [Ca2+](i) (73 +/- 22 and 61 +/- 18 nM, respectively) in Jurkat: cell populations that was independent of external Ca2+. In individual cells, caffeine and ryanodine induced Ca2+ spikes. Jurkat cell populations initially exposed to caffeine did not respond further to ryanodine and vice versa, suggesting an overlap of the Ca2+ pool that was contained within the thapsigargin sensitive Ca2+ reserve. [H-3]ryanodine bound to a single class of sites of Jurkat microsomes (K-D, 18.4 +/- 5.7 nM; B-max 24.3 +/- 7.7 fmol/mg protein). Photolytic release (Nitr5) of caged Ca2+ induced a time-dependent increase of Ca2+ in individual Jurkat cells. The profile of the release of Ca2+ was characterized, 1) by a kinetic (0.55 +/- 0.07 nM s(-1)) slower than the Ca2+ response to caffeine (3.93 +/- 0.66 nM s(-1)) or to ryanodine (3.96 +/- 0.94 nM s(-1)), 2) by a release of Ca2+ (131 +/- 43 nM) that slowly returned to baseline and during which low amplitude oscillations were present (room temperature) or Ca2+ spikes (37 degrees C) and, 3) by a lack of dependency on an influx of Ca2+. Inhibitors of CICR (ruthenium red and 1-octanol) prevented the photolysis dependent increase in [Ca2+](i) but not the InsP3-dependent Ca2+ response. Our data suggest that Jurkat T cells possess at least two Ca2+ pools, one that is sensitive to InsP3 and one that is insensitive. These two Ca2+ pools may be involved in a CICR that generates spontaneous Ca2+ spikes and oscillations in these cells. (C) 1997 Elsevier Science Inc.